.img {
    width: 100%;
    height: 100%;
    overflow: hidden;
    position: relative;
}

img {
    width: 100%;
    height: 100%;
    z-index: -1;

}

.dian {
    position: absolute;
    color: #fff;
    top: 50%;
    left: 50%;
    font-size: 50px;
}